4.1 Sexual Reproduction in Humans

State what the male reproductive system consists of

-A pair of testes

• The penis

• Ducts connecting the testes with the penis

• Accessory glands

Function of scrotum

• Maintains a {cool / optimum / 34oC} environment (for spermatogenesis) / Allow temperatures between 34-36 oC

• holds testes outside abdomen

Function of Epididymis

Sperm are stored here and mature to become fully mobile.

Function of testes

• Produce gametes

• Produce testosterone.

Function of Vas deferens

Carries sperm towards the penis during ejaculation.

Function of seminal vesicle

Secretes mucus into the vas deferens that contains a mixture of chemicals which make up approximately 60% of semen.

Function of seminal fluid

• Provides nutrients for sperm

• Alkaline to help neutralise the acidity of the urine remaining in the urethra and the acidity of the vaginal tract.

Function of prostate gland

Secretes a fluid into the vas deferens that contains a mixture of chemicals which make up approximately 30% of semen.

What does seminal fluid contain

fructose and amino acids

What does prostate fluid contain

zinc ions and is also alkaline which helps to neutralise the acidity of any urine remaining in the urethra and the acidity of the vaginal tract.

Function of urethra

• Carries semen through the penis and out of the body.

• Carries urine from the bladder through the penis and out of the body.

Function of penis

Specialised organ adapted to transfer semen to the vagina during sexual intercourse.

What do the testis contain

seminiferous tubules

What do the cells lining the seminiferous tubules undergo

spermatozoa (sperm) formation and throughout the process

What happens when sperm reaches the lumen of the seminiferous tubules

they move through the tubule and collect in the vasa efferentia

Function of vasa efferentia

coiled tubes that carry sperm to the head of the epididymis

What is fructose used for in sperm cells

they are respired for energy

Name the accessory glands

prostate gland and seminal vesicles

Name the fluid that emerges from the prostate gland

semen, a mixture of sperm, seminal and prostate fluid

Function of ovary

• Production of gametes

• Produce oestrogen and progesterone.

Function of Fallopian tubes (oviducts)

They have a lining of ciliated epithelial cells which move the secondary oocyte to the uterus.

Function of uterus

Holds the developing foetus until birth.

Function of Endometrium

It has a good blood supply and builds up every month during the menstrual cycle. If implantation of an embryo does not happen then the endometrium is shed during menstruation.

State the 3 layers of the uterus

- Perimetrium, thin layer around the outside

- Myometrium, the muscle layer

- Endometrium, inner most layer

Function of the cervix

A narrow ring of connective tissue and muscle, it acts as a barrier between the uterus and the outside environment during pregnancy.

How does the cervix prevent entry of pathogens during pregnancy

a mucous plug forms in the cervix which helps prevent entry of pathogens.

Name the production of gametes in the sex organs

gametogenesis

Name the formation of sperm in the testis

Spermatogenesis

Name the formation of secondary oocytes in the ovary

Oogenesis

Why is it important that gametes are haploid

so that at fertilisation, the diploid number is restored and the chromosome number does not double in every generation.

Describe Spermatogenesis

1) Cells of the germinal epithelium are diploid, They divide by mitosis to make diploid spermatogonia and more germinal epithelium cells.

2) Spermatogonia divide many times by mitosis, making more spermatogonia. Some enlarge making diploid primary spermatocytes

3) Primary spermatocytes undergo meiosis I, making secondary spermatocytes, which are haploid

4) Secondary spermatocytes undergo meiosis II, making haploid spermatids

5) Spermatids mature into spermatozoa or sperm

What does the head of a sperm cell contain

a haploid nucleus, covered at the anterior end by a lysosome, called acrosome which contain enzymes used at fertilisation

Describe the middle piece of a sperm cell

packed with mitochondria which spiral around the microtubules which extend from the centrioles into the axial filament in the tail

Function of mitochondria in a sperm cell

Provide ATP for movement

Function of the flagellum in a sperm cell

makes lashing movements that move the sperm

When do sperm cells become motile

when they have been modified in the epididymis

Where does spermatogenesis occur

in the germinal epithelium of the seminiferous tubules

Function of Sertoli cells

Provide mechanical support, nutritional support and immune support

Function of interstitial cells

secrete testosterone

Function of germinal epithelium

Undergo mitosis and meiosis to produce gametes

location of fimbriae

entrances of oviduct funnel

Function of fimbriae

Sweep secondary oocyte into the oviduct

Location of ciliated epithelial

Lining the oviduct

Function of ciliated epithelial

Convey the secondary oocyte to the uterus

Location of endometrium

Innermost layer of uterus

Function of endometrium

Secretes mucus to aid implantation

What lines the basement membrane inside the seminiferous tubule

spermatogonia

What kind of cell is spermatogonia

stem cells

Outline what happens in oogenesis before birth

1) Cells of the germinal epithelium of the ovary, which are diploid, divide by mitosis to make diploid oogonia and more germinal epithelium cells.

2) The oogonia divide many times by mitosis and enlarge, making diploid primary oocytes and more oogonia

3) The primary oocytes begin meiosis I but are arrested in its progress at prophase I

4) Germinal epithelium cells divide to form diploid follicle cells which surround the primary oocytes, making primary follicles

Outline the stages of oogenesis after puberty

1) Hormones stimulate the primary follicles to develop further. A primary oocyte completes meiosis I, making a secondary oocyte. The other product is the first polar body.

2) The primary follicle develops into a secondary follicle. It migrates to the surface of the ovary where it bursts and releases the secondary oocyte, in a process called ovulation

3) The secondary oocyte begins meiosis II but stop s at metaphase II unless fertilisation takes place

Outline the stages of oogenesis after fertilisation

Meiosis II is completed, making an ovum containing most of the cytoplasm. The other product of meiosis II is the second polar body

Outline the stages of oogenesis after ovulation

The mature secondary follicle (Graafian follicle) becomes the corpus luteum (yellow body)

What usually happens to the first polar body

disintegrates immediately

What's the germ cell in females called

oogonium

Where does fertilisation take place

in the fallopian tube

What process needs to happen before a sperm cell can fertilise a secondary oocyte

Capacitation

Describe what occurs in capacitation

• Cholesterol and glycoproteins are removed from the cell membrane over the acrosome of the sperm head.

• The membrane is thinned becomes more fluid and more permeable to calcium ions

• The tail motion changes to a whipping motion, increasing sperm motility

Describe the acrosome reaction

• Sperm bind to receptors in the zona pellucida which initiates the reaction

• The acrosome releases several lysosomal enzymes which digest the cells of the corona radiata.

• Then on contact with the zona pellucida, the acrosome membrane ruptures and releases more lysosomal enzymes which hydrolyses the zona pellucida

Name on enzyme that is releases from the acrosome rupturing

acrosin

What are the 2 protective layers the sperm must penetrate

Corona radiata and the zona pellucida

State the outcome of the acrosomal reaction

• a single sperm contacts one of the sperm binding receptors on the oocyte’s plasma membrane

• The plasma membrane of the sperm fuses with the plasma membrane of the oocyte.

• The sperm nucleus is transferred to into the secondary oocyte

• The completion of the second meiotic division of the oocyte nucleus occurs

After the entry of the sperm head what is the secondary oocyte called

ovum

How does the oocyte prevent polyspermy

• Cortical reaction

• Produces a fertilisation membrane

• The oocyte’s smooth ER releases calcium ions into the cytoplasm

• Cortical granules fuse with the cell membrane and release their contents of enzymes.

• The zona pellucida hardens and expands

What does the fusion of the ovum and sperm form

diploid zygotic nucleus

Define polyspermy

Entry of additional sperm

How is the zygote projected toward the uterus

by peristalsis and beating cilia

What results in the zygote having more cells

Cleavage

What is each daughter cell that is produced by cleavage is called

blastomere

What is the name given to the structure made by the 16-cell embryo that reaches the uterus

morula

Once inside the uterus what does the morula do

it secretes fluid

organises around a fluid filled cavity, the blastocoel

What is the name of the morula after it organises around the blastocoel

blastocyst

What does the group of cells within the blastocyst form

inner cell mass

What is the name of the cells that from the outer layer of the blastocyst

trophoblast

What do the trophoblasts develop into

the chorionic sac and the foetal portion of the placenta

The inner mass of embryonic cells is …… in implantation

totipotent

Define totipotent

Each cell has the potential to differentiate into any cell type in the human body

How do the outer layers of the blastocyst grow into the endometrium

by digesting the endometrial cells and wound healing of the endometrium to close up the blastocyst into the tissue

What does the chorion layer of the blastocyst release

Human chorionic gonadotropin

What does HCG do

keeps the corpus luteum active

Structure of Female Reproductive System

Structure of Male Reproductive System

Structure of Ovary

Structure of Secondary oocyte

Structure of Blastocyst

State the function of trophoblastic villi on the blastocyst

increase surface area for the absorption of nutrients from the endometrium

Structure of Graafian follicle

How does the placenta connect to the conceptus

umbilical cord

In the umbilical cord , what is deoxygenated blood and metabolic waste carried through

Through two umbilical arteries away from the foetus

In the umbilical cord what is nutrients and oxygen carried through

The single umbilical vein returning to the foetus

What does the trophoblast develop into

The amnion and chorion

What does the chorion develop

finger-like processes called chorionic villi

Properties of the chorionic villi

• Microvilli which increase surface area

• Thin walls for a short diffusion distance

• Counter current flow between the foetal and maternal blood which maintains a concentration gradient.

How does the foetal and maternal blood not commingle

Blood cells cannot move across the placenta

Why is it important that the foetal and maternal blood doesn’t commingle

• Separates mother’s cytotoxic T cells from destroying the foetus

• Ensures Foetal red blood cells do not enter the mother’s circulation and trigger antibody development

Why is it important that there is a physical barrier between the foetal and maternal circulation

• Protects the fragile, foetal capillaries from damage by the higher blood pressure of mother.

• Protects developing foetus from the change sin maternal blood pressure

Describe the placenta’s role as an endocrine gland

During the second trimester the placenta has taken over the production of oestrogen and progesterone from the corpus luteum which has degenerated

How does the placenta provide immunity to the foetus

maternal antibodies cross the placenta and attack pathogens

Where does the umbilical cord develop from

the placenta

What are hormones

Chemical messengers produced by endocrine glands

How are hormones transported

by the blood